1. Technical Field
The present invention relates to a liquid ejection apparatus such as an inkjet printer.
2. Background Art
Typically, an inkjet printer is known as a liquid ejection apparatus that ejects liquid from a recording head, or a liquid ejection head, onto a target. The inkjet printer ejects ink onto a recording paper sheet as a target. The printer includes a recording head and a transport mechanism. The recording head is mounted in a carriage that reciprocates in a main scanning direction. The transport mechanism transports the recording paper sheet in a sub scanning direction. Nozzles are formed in the recording head for ejecting the ink, which is supplied from a cartridge (a liquid retaining body), onto the recording paper sheet.
A predetermined amount of ink is retained in the cartridge. The retaining amount of the ink gradually decreases as printing on the recording paper sheet is repeated. Japanese Laid-Open Patent Publication No. 2000-158665 describes a printer that indicates the need for replacement by a unused cartridge when the retaining amount of the ink in the cartridge becomes less than or equal to a predetermined threshold value.
The printer of Japanese Laid-Open Patent Publication No. 2000-158665 is an off-carriage type in which the cartridge is installed in a component other than a carriage. The ink is retained in an ink pack in the cartridge and flows to a recording head through an ink supply line through hydraulic head of the ink in the ink pack with respect to the recording head. The hydraulic head value P representing the hydraulic head applied to each nozzle of the recording head is obtained by the following equation:P=p3−(p1+p2)
In the equation, p1 represents total resistance acting on the ink that has flown through the ink supply line from an ink pack side end to a recording head side end, which is dynamic pressure of the ink. p2 represents stiffness resistance of the ink pack. p3 represents the difference between the hydraulic head at an ink outlet of the ink pack and the hydraulic head in a nozzle of the recording head.
When printing by the printer of the aforementioned document is being performed or after such printing is completed, it is determined whether the hydraulic head value P is less than or equal to a minimum value that allows ink ejection from the nozzles of the recording head P (hereinafter, referred to as a “critical hydraulic head”). If it is determined that the pressure hydraulic head value P is less than or equal to the critical hydraulic head, it is indicated that the retaining amount of the ink in the ink pack is less than or equal to the threshold value. The critical hydraulic head is a predetermined fixed value. The threshold value is set in correspondence with the critical hydraulic head. The dynamic pressure p1 of the ink and the stiffness resistance p2 of the ink pack vary in correspondence with the temperature in the proximity of the printer (hereinafter, referred to as an “environmental temperature”), the length of the ink supply line, viscosity of the ink, and the remaining amount of the ink in the ink pack. Nonetheless, the dynamic pressure p1 of the ink and the stiffness resistance p2 of the ink pack are set to values determined under the most undesirable conditions.
The dynamic pressure p1 of the ink and the stiffness resistance p2 of the ink pack, with which the hydraulic head value P is calculated, increase as the environmental temperature drops. Therefore, the printer of the aforementioned publication sets the dynamic pressure p1 of the ink and the stiffness resistance p2 of the ink pack to values corresponding to a lower temperature (for example, 10° C.) to avoid ink shortage when printing is being carried out.
However, if the actual environmental temperature of the printer is higher (for example, 25° C.), the dynamic pressure p1 of the ink and the stiffness resistance p2 of the ink pack, which are set to the aforementioned values corresponding to the lower temperature, exceed the values corresponding to the actual environmental temperature. As a result, regardless of that a sufficient amount of ink is retained in the ink pack, it may be determined that the hydraulic head value P is less than or equal to the critical hydraulic head. In other words, the printer may indicate the need for replacement of the cartridge regardless of the sufficient retaining amount of the ink in the ink pack.